Method for operating a heat pump system, heat pump system and hvac system

ABSTRACT

The invention relates to a method for operating a heat pump system, a heat pump system and an HVAC system measuring a solar irradiance, wherein the operation of the heat pump is adjusted based on the solar irradiance.

FIELD OF THE INVENTION

The disclosure relates to a method for operating a heat pump system, aheat pump system and an HVAC system measuring a solar irradiance,wherein the operation of the heat pump is adjusted based on the solarirradiance.

BACKGROUND OF THE INVENTION

In recent years heat pump systems have become very popular mainly due totheir high efficiency. They are therefore regarded as a key renewablesolution for zero energy houses. In conventional heat pump systems theheat pump is usually controlled based on an indoor air temperaturemeasurement as shown in FIG. 1. A set indoor temperature T_(set) isinput into the control procedure and feed-forward control 1 as well asfeed-back control 2 are employed to achieve a target flow temperature ofa heat transport medium flowing in the heat pump system. An ambienttemperature T_(amb) enters the feed-forward control. The target flowtemperature then is usually input into a limiter 3 and the resultingtarget flow temperature limited of power is input into an emitter 4which outputs a supplied flow temperature being provided to the building5 resulting in a room temperature T_(room).

The heating control comprises two parts, the feed-forward control (FFcontrol) 1 as well as the feed-back control (FB control) 2. These arecommonly implemented in heat pump systems. Preferably the feed-forwardcontrol calculates the target flow temperature T_(water) using the setroom temperature T_(set) and the ambient temperature T_(amb). Thefeed-back control calculates an adjustment value of the target flowtemperature T_(water) using a deviation between the target roomtemperature T_(set) and a measured room temperature.

Usually the room temperature is measured for example by a wirelessremote controller, the location of which varies in actual applications.This results into an uncertainty of the room temperature measurements interms of delay due to the non-uniformity of the indoor temperature,caused for example by solar flux near the fenestration. Furthermore,conventional heating systems tend to overheat a room due to thelimitation of feed-back control and the nature of solar gain to a house.

SUMMARY OF THE INVENTION

It is therefore the problem to be solved by the present disclosure toimprove the temperature control of a heat pump in case of solarirradiation onto a building.

This problem is solved by the method for operating a heat pump systemaccording to claim 1, the heat pump system according to claim 10 and theheating, ventilation and air conditioning, HVAC, according to claim 14.

The present disclosure relates to a method for operating a heat pumpsystem. The method according to the disclosure can in principle beapplied to any kind of heat pump system. Such a heat pump system forexample comprises a heat pump as well as a heat transport mediumcircuit, conducting a heat transport medium. The heat transport mediumcan be heated or cooled by the heat pump. The heat pump can for examplecomprise a refrigerant circuit in which a condenser, an expansion valve,an evaporator and a compressor are connected to each other in series byrefrigerant conduits. It should be stressed that the configuration ofthe heat pump is not essential for the disclosure. The disclosure can beapplied to all means for heating or cooling rooms. Here the term “heatpump” shall stand for a device heating an indoor room as well as adevice for cooling an indoor room. The term “air conditioner” can alsobe used.

The method for operating a heat pump system according to the disclosurecomprises measuring a solar irradiance incident onto a building. Thesolar irradiance can be measured by a suitable sensor. Since solar lightimpinges onto earth in a homogenous distribution a localized measurementof the solar irradiance is usually sufficient. The total energy broughtinto a building by solar irradiance can than be determined based on thislocalised measurement together with an effective model of the building.Where reference is made to solar irradiance, alternative terms can beused, as for example solar flux and solar energy density.

The method of the present disclosure then adjusts an operation of a heatpump included in the heat pump system based on the measured solarirradiance. Preferably the operation of the heat pump is adjusted onlywhen the solar irradiation is larger than a predetermined threshold.

In a preferred embodiment of the disclosure the operation of the heatpump can be adjusted using feed-forward control and/or feed-backcontrol. In this case, a temperature correction amount ΔT can becalculated based on the measured solar irradiation to adjust quantitieswhich enter the feed-forward control and/or the feed-back control.

One quantity which can preferably be adjusted by the temperaturecorrection ΔT is the target flow temperature of the heat pump. This isfor example the designated temperature of a heat transfer medium whichis heated by the heat pump. The feed-forward control and/or thefeed-back control aim to achieve the target flow temperature. Thus, ifthis value is changed also the operation of the heat pump is changed. Assolar irradiation enters energy into a building, an increased solarirradiation preferably results in a reduction of the target flowtemperature.

A further quantity which can be advantageously used to adjust theoperation of the heat pump is the air temperature set point of an indoorair temperature. This is the temperature which is desired within theroom. It is set for example at a thermostat. If solar irradiationintroduces energy into a room, less heat is to be provided by the heatpump. If the heat pump is controlled using feed-forward control and/orfeed-back control, this can be achieved by reducing the actually settemperature by the temperature correction ΔT. Thus, a user will set acertain temperature T_(indoor sp) but an adjusted value T_(indoor sp)−ΔTenters the feed-forward and the feed-back control.

In an advantageous embodiment of the disclosure the operation of theheat pump can be adjusted by adjusting the operating frequency of acompressor included in the heat pump. The higher the operating frequencyis, the higher is the amount of heat provided by the heat pump.Increased solar irradiance will therefore usually lead to a reducedoperating frequency of the compressor.

In an advantageous embodiment of the disclosure the operation of theheat pump can be adjusted using feed-forward control and/or feed-backcontrol, and can further comprise a step of comparing the measured solarirradiance ΔT to a predetermined threshold irradiance. By this step itcan be ensured that adjustment is only performed if the solar irradianceis sufficiently significant.

The irradiance threshold ϕ_(threshold) can be set, for example,according to building properties such as fenestration (that is, thenumber and size of windows) and the thermal mass (which can, forexample, be estimated using a standard such as the Standard AssessmentProcedure SAP 2012).

If in this case the measured solar irradiance ϕ is equal or larger thanthe threshold irradiance a solar gain Q_(solar) can be determined asQ_(solar)=αϕ, where α is a solar aperture coefficient, which for examplecan be derived from TAITherm simulation results. It is then preferablypossible to determine a flow temperature reduction ΔT as ΔT=Q_(solar)/(mC_(p)). Here m is a mass flow rate of a heat transfer fluid of the heatpump system, and T_(p) is a specific heat capacity of the heat transfermedium of the heat pump system. The operation of the heat pump can thenbe adjusted by reducing the target flow temperature T_(flow,supply) ofthe heat pump by ΔT.

In a further preferred embodiment of the disclosure the operation of theheat pump can be adjusted using feed-forward control and/or feed-backcontrol. In this embodiment the method can further comprise comparingthe measured solar irradiance ϕ to a threshold irradiance. If themeasured solar irradiance ϕ is equal to or larger than the thresholdirradiance, a solar gain Q_(solar) can be determined as Q_(solar)=αϕ,wherein α is again the solar aperture coefficient. It is then preferablypossible to determine an air temperature reduction as ΔT=Q_(solar)/M,wherein M is a thermal mass of the building. The operation of the heatpump can then be adjusted by reducing the indoor temperature set pointT_(indoor sp) by ΔT and using the reduced indoor temperature set pointin the feed-forward control and/or the feed-back control.

It is preferred to measure the solar irradiance by a solar irradiancesensor which is located on the outside of the building, preferably at ahighest point of the building or at a spot of the building having anunobstructed view to the sun during the whole day.

It is preferable that the solar sensor has an unobstructed view forreceiving sunlight in order to receive a maximum amount of solarirradiation. The solar sensor should therefore not be installed in alocation that is shadowed by other buildings, trees, or other objects.It is particularly preferred to install the sensor on the top of thebuilding or on a separate mounting close to the building. If the sensorneeds to be installed on an external wall or window, it is preferredthat this is the wall or window the receives the greatest amount ofsunlight. In the northern hemisphere this would be, for example, asouthward-facing wall or window.

Preferably the method of the present disclosure is carried outrepeatedly, in particular preferably at least once every hour,preferably at least once every fifteen minutes, in particular preferablyat least once every minute.

The present disclosure furthermore relates to a heat pump systemcomprising at least one heat pump as well as at least one sensorconfigured for measuring a solar irradiance onto a building. The heatpump can for example be configured as described above.

The heat pump system according to the disclosure furthermore comprises acontroller which is configured to control an operation of the at leastone heat pump based on an amount of solar irradiance measured by the atleast one solar irradiance sensor.

It is in particular preferred if the controller is configured to adjustan operating frequency of a compressor included in the at least one heatpump. This controlling of the operating frequency of the compressor isthen the control of the operation of the at least one heat pump based onthe solar irradiation.

The solar irradiance sensor can for example be a silicon photo cell or athermal pile type sensor. Silicon photocells are cheaper thanthermopile-type sensors and are therefore preferred for the presentdisclosure.

It is particularly preferred if the heat pump is configured to carry outa method as described above.

The present disclosure also refers to an HVAC system including the heatpump system described above.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the disclosure will be described by way of exampleswith reference to figures. The features described in the context of theexamples can also be realized independently from the specific example.

FIG. 1 shows a functional diagram of an auto-tuning-feed-forward controland feed-back control of the prior art,

FIG. 2 shows the effect of the present disclosure,

FIG. 3 shows a control diagram of a heat pump operating method in whichthe target flow temperature is adjusted,

FIG. 4 shows a control algorithm for the flow temperature set pointadjustment in FIG. 3,

FIG. 5 shows a control diagram of a heat pump operation in which theindoor temperature set point is adjusted, and

FIG. 6 shows a control algorithm of the indoor temperature set pointadjustment in FIG. 5.

DESCRIPTION OF EMBODIMENTS

Calculating solar heat gain is a process that involves details aboutwindow size, orientation, shading, and material properties along withestimates of direct and indirect solar irradiance. Solar gain can beexpressed by the Equations (1)-(6) [ASHRAE Research, ASHRAEHandbook—Fundamentals; Atlanta: ASHRAE 2017].

$\begin{matrix}{\mspace{79mu} {q_{s} = {E_{DN}{\cos (\theta)}\left( {T - {NA}} \right)W_{A}}}} & (1) \\{\mspace{79mu} {{{SHGC}\left( {\theta,\lambda} \right)} = {{T\left( {\theta,\lambda} \right)} - {{NA}\left( {\theta,\lambda} \right)}}}} & (2) \\{\mspace{79mu} {q_{s} = {E_{DN}{\cos (\theta)}{{SHGC}\left( {\theta,\lambda} \right)}W_{A}}}} & (3) \\{\mspace{79mu} {{{SHGC}(\theta)} = {{T(\theta)} - {\sum\limits_{k = 1}^{L}{N_{k}A_{k}}}}}} & (4) \\{\mspace{79mu} {q_{s} = {I \times {{SHGC}_{e}(\theta)} \times {AR}_{e}}}} & (5) \\{{\cos (\theta)} = {{{\sin (\delta)}{\sin (\varphi)}{\cos (\beta)}} - {{\sin (\delta)}{\cos (\varphi)}{\sin (\beta)}} - {{\cos (\delta)}{\cos (\varphi)}{\cos (\beta)}{\cos (\omega)}} - {{\cos (\delta)}{\sin (\varphi)}{\sin (\beta)}{\cos (\gamma)}{\cos (\omega)}} - {{\cos (\delta)}{\sin (\beta)}{\sin (\gamma)}{\sin (\omega)}}}} & (6)\end{matrix}$

Since total solar readings were recorded normally and also in variousdata sources, it is necessary to split the total radiation into directand diffuse components [2].

I/I ₀=1.0−0.09k _(T), for k _(T)≤0.22  (7)

I/I ₀=0.9511−0.1604k _(T)+4.388k _(T) ²−16.638k _(T) ³+12.366k _(T) ⁴,for 0.22<k _(T)≤0.8  (8)

I/I ₀=0.165, k _(T)>0.8  (9)

In an advantageous embodiment the solar heat gain introduced into abuilding can be determined from the measured solar irradiance using asolar feed gain coefficient, SHGC, method.

Data that actually provided by a manufacturer of windows typicallyinclude:

-   -   Number of layers—single pane, double or triple pane?    -   Description of the glass type—coloration, whether or not it has        low E coating    -   U-factor (NFRC2004b)    -   Solar Heat Gain Coefficient(SHGC) at normal incident angle    -   Visual transmittance

Preferably, conduction heat gain is computed separately from thetransmitted and absorbed solar heat gain. Because the thermal mass ofglass is normally very low, the conduction is approximately steadystate. Accordingly, the conduction heat gain may be calculated as:

q _(cond) =UA(T _(outdoor) −T _(indoor))  (10)

Transmitted and absorbed solar heat gains are advantageously calculatedas follows:

1. Compute the incidence angle, surface azimuth angle, incident directirradiation and diffuse irradiation on windows;2. If exterior shading exists, determine sunlit area and shaded area;3. For windows without shading, the beam and diffuse and total heat gainare given:

q _(SHG,Direct) =E _(Direct) A _(unshaded)SHGC(θ)  (11)

q _(SHG,Diffuse)=(E _(Diffuse) +E _(reflected))A_(total)SHGC_(diffuse)  (12)

q _(SHG,) =q _(SHG,Direct) +q _(SHG,Diffuse)  (13)

whereSHGC(θ) is the angle dependent SHGC interpolated as in Table 1.

TABLE 1 Window optical properties and SHGC Hemi- Angle 0 10 20 30 40 5060 70 80 90 spherical Single pane, 3 mm thick, clear τ_(sol) 0.834 0.8330.831 0.827 0.818 0.797 0.749 0.637 0.389 0 0.753 α₁ 0.091 0.092 0.0940.096 0.100 0.104 0.108 0.110 0.105 0 0.101 SHGC 0.859 0.859 0.857 0.8540.845 0.825 0.779 0.667 0.418 0 0.781 Double pane, both panes 3.2 mmthick with low e coating, inner pane 5.7 mm thick τ_(sol) 0.408 0.4100.404 0.395 0.383 0.362 0.316 0.230 0.106 0 0.338 α₁ 0.177 0.180 0.1880.193 0.195 0.201 0.218 0.239 0.210 0 0.201 α₂ 0.06 0.060 0.061 0.0610.063 0.063 0.061 0.053 0.038 0 0.059 SHGC 0.469 0.472 0.466 0.459 0.4480.428 0.382 0.291 0.152 0 0.400 Double pane, both panes 5.7 mm thick,clear τ_(sol) 0.607 0.606 0.601 0.593 0.577 0.546 0.483 0.362 0.165 00.510 α₁ 0.167 0.168 0.170 0.175 0.182 0.190 0.200 0.209 0.202 0 0.185α₂ 0.113 0.113 0.115 0.116 0.118 0.119 0.115 0.101 0.067 0 0.111 SHGC0.701 0.701 0.698 0.691 0.678 0.648 0.585 0.456 0.237 0 0.606 Note: Datagenerated with the WINDOW program [4].

Another advantageous method for calculating the solar heat gain is forexample the overall solar aperture coefficient method.

This method is for example used in co-heating tests which involve thecreation of a further whole building parameter, the solar aperture,(A_(sol (m) ²)), defined by its use within the regression process andthe measurement of incident solar radiation. The term A_(sol) is welldefined by P. Baker, “A retrofit of a Victorian terrace house in NewBolsover: a whole house thermal performance assessment,” HistoricEngland & Glasgow Caledonian University, 2015, which refers to the solaraperture as the ‘heat flow rate transmitted through the buildingenvelope to the internal environment under steady state conditions,caused by solar radiation incident at the outside surface, divided bythe intensity of incident solar radiation in the plane of the building.It can be regarded as equivalent to a totally transparent area whichlets in the same solar energy as the whole building’.

As the total heat flow across the building fabric cannot be measureddirectly, the co-heating method uses a simplified energy balanceequation to infer heat loss as shown equation (14) in an unoccupiedhouse.

$\begin{matrix}{{Q_{active} + Q_{sol}} = Q_{loss}} & (14) \\{{Q_{active} + {A_{sol} \cdot I_{sol}}} = {{HLC} \cdot \left( {T_{indoor} - T_{outdoor}} \right)}} & (15) \\{Q_{active} = {{{HLC} \cdot \left( {T_{indoor} - T_{outdoor}} \right)} - {A_{sol} \cdot I_{sol}}}} & (16) \\{\frac{Q_{active}}{T_{indoor} - T_{outdoor}} = {{{- A_{sol}} \cdot \frac{I_{sol}}{T_{indoor} - T_{outdoor}}} + {HLC}}} & (17)\end{matrix}$

Q_(active) is the heat supplied either by electric or heat pump, W.HLC is the heat loss coefficient, W/K.Based on measured parameters and the HLC and A_(sol) can be obtained ina long period of tests.

The value of A_(sol) is a function of not only glazing characteristicsof the dwelling but also its thermal mass.

A further advantageous method for determining the solar heat gain is thestandard assessment procedure, SAP.

As described in BRE, The Government's Standard Assessment Procedure forEnergy Rating of Dwellings (SAP 2012), Garston: BRE, 2017. Solar gainsare calculated using solar flux from U3 in Appendix U and associatedequations to convert to the applicable orientation.

G _(solar)=0.9×A _(w) ×S×g _(⊥) ×FF×Z

Where

G_(solar) is the average solar gain, W;0.9 is the factor repenting the ratio of typical average transmittanceto that at normal incidence;A_(w) is the area of an opening (a window or a glazed door), m2;S is the solar flux on the applicable surface, W/m2;g_(⊥) is the total solar energy transmittance factor of the glazing atnormal incidenceFF is the frame factor for windows and doors (fraction of opening thatis glazed);Z is the solar access factor.The factors can be estimated in Tables 2, 3 and 4.

TABLE 2 Transmittance factors for glazing Total Light Glazing solarenergy transmittance, Type transmittance, g_(⊥) g_(L) Single glazed 0.850.9 Double glazed (air or argon filled) 0.76 Double glazed (low-E,hard-coat) 0.72 Double glazed (low-E, soft-coat) 0.63 {close oversizebrace} 0.8 Window with secondary glazing 0.76 Double glazed (air orargon filled) 0.68 Double glazed (low-E, hard-coat) 0.64 {close oversizebrace} 0.7 Double glazed (low-E, soft-coat) 0.53

TABLE 3 Frame factors Frame Type Frame Factor Wood 0.7 Metal 0.8 Metal,thermal break 0.8 PVC-U 0.7

Note: if know the actual frame factor should be used instead of the datain the Table.

TABLE 4 Solar and light access factors % of sky blocked Winder solarSummer solar Light access Overshading by obstacles access factor* accessfactor** factor Heavy >80% 0.3  0.5 0.5  More than >60%-80% 0.54 0.70.67 average Average or  20%-60% 0.77 0.9 0.83 unknown Very little <20%1.0  1.0 1.0  Note: *for calculation of solar gains for heating. **forcalculation of solar gains for cooling and summer temperatures.

FIG. 2 shows the effect of the present disclosure. FIG. 2(a) shows theair temperature and the solar irradiance throughout the day in the upperdiagram and the compressor frequency and the heat pump power throughoutthe day in the lower diagram for a prior art heat pump control. FIG.2(b) shows the air temperature and solar irradiance over the course ofthe day in the upper diagram and the compressor frequency and heat pumppower over the day in the lower diagram for a heat pump systemcontrolled according to the present disclosure.

In the upper diagrams of FIGS. 2(a) and 2(b) the full line indicates thesolar irradiance, the short dashed line indicates the ambienttemperature and the long dashed line indicates the set point indoortemperature. In the lower diagrams of FIGS. 2(a) and 2(b) the thick fulllines indicate the heat pump power and the thin full lines indicate thecompressor frequency.

The solar irradiance starts increasing with sunrise, reaches its maximumat noon and reaches zero at sunset.

As in the prior art the heat pump is controlled based on the measuredindoor temperature, the compressor frequency in FIG. 2(a) is reduced ata time t₀ where the indoor temperature starts to increase. At a time t₁the compressor is fully shut down if the indoor temperature reaches acertain value. The heat pump power follows the compressor frequency inthe lower diagram of FIG. 2(a).

In FIG. 2(b) showing the effect of the disclosure the heat pumpoperation is controlled based on the measured solar irradiance. If at atime t₀′ the solar irradiance increases above a threshold irradiance thecompressor frequency f is reduced and at the same time the heat pumppower is reduced. If at a time t₁′ the solar irradiance increases abovea further threshold the compressor frequency f is set to zero andcorrespondingly the heat pump power becomes zero. It can be seen in theupper diagram of FIG. 2(b) that the indoor temperature, represented bythe full line, stays closer to the set point temperature indicated bythe long dashed line than in the conventional control shown in the upperdiagram of FIG. 2(a). Furthermore, it can be seen that the compressorfrequency is reduced at the earlier times to and t₁′ than the times t₀and t₁ in the conventional control method. Therefore, energy of the heatpump operation is saved as indicated by the hashed regions in the lowerdiagram of FIG. 2(b).

FIG. 3 shows a control diagram of a method for operating a heat pumpsystem according to the disclosure. The method employs a feed-forwardcontrol 1 as well as a feed-back control 2. On the left side a set roomtemperature enters firstly an optional low pass filter 6 and then entersthe feed-forward control 1 where together with a measured ambienttemperature a target flow temperature is calculated. The output of thelow pass filter 6 is furthermore input into the feed-back controlelement 2 which also produces a target flow temperature. The target flowtemperature provided by the feed-forward control 1 and the feed-backcontrol 2 are combined to a resulting target flow temperature. Thisresulting target flow temperature is in this embodiment adjusted in step8 based on a solar irradiance measured by a suitable solar irradiancesensor. Step 8 outputs an adjusted target flow temperature. Thisadjusted target flow temperature goes through the power safe control 3,the outdoor unit 4 and the house 5 to result in a room temperature. Theroom temperature is fed back via the low pass filter 7 to the input ofthe feed-back control so that the difference between the set roomtemperature output by the low pass filter 6 and the fed back roomtemperature output by the low pass filter 7 is input into the feed-backcontrol 2.

The Power save control 3 is a function to reduce the compressorfrequency fluctuation, in order to smoothen the operation and thus savepower consumption due to sudden change of compressor frequency. Outdoorunit 4 is the block of a heat pump outdoor unit with the mainrefrigeration cycle, which operates in outdoor environment to absorb thelow grade energy from the ambient such as air or ground. House 5 is ablock representing the building which requires heat supplied from heatpump for maintaining a certain temperature.

FIG. 4 shows a flow diagram of an algorithm carried out in the controldiagram of FIG. 3. In a first step S1 an indoor temperature in a roomheated by the heat pump is measured. Furthermore, in a step S2 anambient temperature is measured, which is for example an outdoortemperature. It should be noted that although steps S1 and S2 are shownin a certain sequence in FIG. 4, they can be carried out in differentorder and also at the same time.

In step S3 an initial temperature T_(flow,supply) is calculated. Thisinitial T_(flow,supply) is provided from the input value from theprevious block indicated as target flow temperature in FIG. 3. Thisvalue is initially calculated from the feed-forward control block 1 andthe feed-back control block 2 in FIG. 3.

In a step S4 a solar flux ϕ is acquired, for example by a sensor or byother web based data. A dimension of the solar flux is for example W/m².It should be noted that in FIG. 4 step S4 is shown after step S3.However, the solar flux ϕ could as well be acquired at any other pointof the sequence of steps S1, S2 and S3.

The following steps S5, S6, S7, S8 and S9 are carried out in block 8 inFIG. 3.

In step S5 it is decided whether the acquired solar flux ϕ is greaterthan a threshold irradiation, for example ϕ_(threshold)=50 W/m². If thisis not the case, the target flow temperature T_(flow,supply) is notmodified. If, on the other hand, the measured solar flux ϕ is greaterthan the threshold flux ϕ_(threshold), step S6 is carried out, where asolar gain Q_(solar) is estimated as Q_(solar)=αϕ. In this example, thesolar gain Q_(solar) [W] absorbed in the building is estimated. Here,the solar aperture coefficient α [m²] and the coefficient can bederived, for example, by a regression method in co-heating tests orcontinuous heating tests of a certain duration.

The estimated solar gain Q_(solar) is then used in step S7 to estimate aflow temperature reduction ΔT as ΔT=Q_(solar)/(mC_(p)). Using this valuein step S8, the target flow temperature T_(flow,supply) is adjusted bysubtracting the flow temperature reduction ΔT, that is,T_(flow,supply):=T_(flow,supply)−ΔT. In step S9, the target flowtemperature is then updated and can be used for the control of the heatpump.

In step S7, the temperature adjustment is calculated based on the solargain Q_(solar) divided by the mass flow rate of the fluid m [kg/s], andthe specific heat capacity of the fluid C_(p) [J/(kg−K)], such as glycolwater.

In step S8, the new flow temperature supplied to the building by theheat pump is reduced by ΔT.

FIG. 5 shows a control diagram of a method for operating a heat pumpaccording to a further embodiment of the disclosure. FIG. 5 correspondsto FIG. 3, but does not have the block 8 in which the target flowtemperature is adjusted in FIG. 3, but instead has an additional block 9where an indoor temperature set point is adjusted based on acquiredsolar irradiance. Regarding blocks 1 to 7, reference is made to FIG. 3.

A set temperature is input into the control, and this set temperature isthen adjusted in block 9 before being input into the low pass filter 6.

An algorithm carried out in block 9 is shown in FIG. 6. Again, in stepsS1, S2, and S4 an indoor temperature in a room to be heated by the heatpump is measured, an ambient temperature, for example an outdoortemperature, is measured, and a solar flux ϕ is acquired. Steps S1, S2,S4 can be carried out in any order and also at the same time. Again, thesolar irradiance ϕ [W/m²] can, for example, be acquired by an installedsensor or by web-based data.

In step S5 the acquired solar flux ϕ is then compared to a thresholdϕ_(threshold), for example ϕ_(threshold)=50 W/m², in order to judgewhether the solar irradiance is sufficiently significant.

If that is the case, in step 6 the solar gain Q_(solar) is estimated asQ_(solar)=αϕ. In this embodiment, as also in the other embodiments, αfor example be derived from TAITherm simulation results.

The estimated solar gain Q_(solar) is then used in step S10 to estimatethe indoor temperature reduction ΔT as ΔT=Q_(solar)/M, wherein M [W/K]is the thermal mass of the building, for example according to SAP orsome other standard.

Using this temperature reduction ΔT, the indoor temperature set pointT_(indoor,sp) is then reduced as T_(indoor,sp):=T_(indoor,sp)−ΔT. Thecorrected value is then updated in step S9 to be used for the furthercontrol of the heat pump as shown in FIG. 5, starting in block 6.

In the case where the heat pump heats the indoor space as well as in thecase where the heat pump or air conditioner cools the indoor space, theadjustment of the temperatures will usually be a reduction of thesetemperatures because the solar radiation adds additional heat into theindoor space.

The utilization of solar gain according to the present disclosure allowssaving energy, as it takes a long time for heat pump controllersaccording to the prior art to recognize that there is a significantamount of solar gain, as the prior art controllers only measure theindoor temperature. The solar gain is mainly stored in the thermal masswhen it arrives in the living space.

The present disclosure is capable of avoiding overheating, which usuallyis a problem in conventional heating systems due to the limitation offeedback control and the nature of solar gain to the house. Thedisclosure can minimize overheating.

A heat pump such as employed in the present disclosure can, for example,be an air-to-water (A2W) heat pump or a ground source heat pump (GSHP)or any heat pump incorporating a refrigerant circuit.

1. Method for operating a heat pump system, comprising measuring a solarirradiance incident onto a building, and adjusting an operation of aheat pump included in the heat pump system based on the measured solarirradiance.
 2. Method according to claim 1, wherein the operation of theheat pump is adjusted only when the solar irradiation is larger than apredetermined threshold.
 3. Method according to claim 1, wherein theoperation of the heat pump is adjusted using feed forward control and/orfeedback control, the method further comprising using the measured solarirradiation to adjust, preferably to reduce, at least one of thefollowing quantities entering the feed forward control and/or thefeedback control by a temperature correction amount: a target flowtemperature of the heat pump, a flow temperature set-point and/or an airtemperature set point of an indoor air temperature.
 4. Method accordingto claim 3, wherein in the adjusting of the operation of the at leastone heat pump the temperature correction amount is determined from themeasured solar irradiation using a solar heat gain coefficient, SHGC,method, a Overall Solar Aperture Coefficient Method and/or a StandardAssessment Procedure, SAP.
 5. Method according to claim 1, wherein theoperating frequency of a compressor included in the heat pump isadjusted to adjust the operation of the heat pump.
 6. Method accordingto claim 1, wherein the operation of the heat pump is adjusted usingfeed forward control and/or feedback control, wherein the method furthercomprises comparing the measured solar irradiance ϕ to a thresholdirradiance, if the measured solar irradiance ϕ is equal or larger thanthe threshold irradiance then determining a solar gain as Q_(solar)=αϕ,wherein α is a solar aperture coefficient, determining a flowtemperature reduction as ΔT=Q_(solar)/(m C_(p)), wherein m is a massflow rate of a heat transfer fluid of the heat pump system and C_(p) isa specific heat capacity of the heat transfer medium of the heat pumpsystem and adjusting the operation of the heat pump by reducing a targetflow temperature T_(flow,supply) of the heat pump by ΔT.
 7. Methodaccording to claim 1, wherein the operation of the heat pump is adjustedusing feed forward control and/or feedback control, wherein the methodfurther comprises comparing the measured solar irradiance ϕ to athreshold irradiance, if the measured solar irradiance ϕ is equal orlarger than the threshold irradiance then determining a solar gain asQ_(solar)=αϕ, wherein α is a solar aperture coefficient, determining anair temperature reduction as ΔT=Q_(solar)/M, wherein M is a thermal massof the building and adjusting the operation of the heat pump by reducingthe indoor temperature set point T_(indoor sp) by ΔT.
 8. Methodaccording to claim 1, wherein the solar irradiation is measured by asensor located on the outside of the building, preferably at a highestpoint of the building or at a spot of the building having unobstructedview of the sun during the whole day.
 9. Method according to claim 1,wherein the steps of the method are carried out at least once everyhour, preferably at least once every 15 minutes, preferably at leastonce every minute.
 10. Heat pump system, comprising at least one heatpump, at least one sensor configured for measuring a solar irradianceonto a building, a controller configured for controlling an operation ofthe at least one heat pump based on an amount of solar irradiancemeasured by the at least one solar irradiance sensor for measuring asolar irradiance.
 11. Heat pump system according to claim 10, whereinthe controller is configured to adjust an operating frequency of acompressor included in the at least one heat pump as the operation ofthe at least one heat pump based on the solar irradiation.
 12. Heat pumpsystem according to claim 10, wherein the solar irradiance sensor is asilicon photo cell or a thermopile type sensor.
 13. Heat pump systemaccording to claim 10 wherein the heat pump is configured to carry out amethod according to claim
 1. 14. HVAC system including a heat pumpsystem according to claim 10.